Gregory the Great
Catena Aurea · Lukasevangelium 10
After these things the Lord appointed other seventy also, and sent them two and two before his face into every city and place, whither he himself would come. Therefore said he unto them, The harvest truly is great, but the labourers are few: pray ye therefore the Lord of the harvest, that he would send forth labourers into his harvest. It follows, And he sent them two and two.
(ubi sup.) But not without deep sorrow can we add, but the labourers are few. For although there are who would hear good things, they are wanting who should spread them. Behold the world is full of priests, but seldom is there found a labourer in God’s harvest, because we undertake indeed the priestly office, but we perform not its works.